1. End result 1n or 2n? 2. Daughter cells Distinct or identical? 3. Chiasmata? Yes or no? MeiosisMitosis 4. # of divisions 5. Purpose Growth or germ cells? QUIZ Name___________________

1. End result 1n or 2n? 1n2n 2. Daughter cells Distinct or identical? identicaldistinct 3. Chiasmata? Yes or no? MeiosisMitosis NoYes 4. # of divisions Purpose Growth or germ cells? GrowthGerm cells QUIZ Name___________________

Observable Patterns of Inheritance Chapter 10 Attached or detached earlobes depends on a single _____ A gene has two molecular forms (______) Inherit one form each _______ Dominant allele specifies detached earlobes

Earlobe Variation You inherited one allele for this gene from each parent _______ allele specifies detached earlobes __________ allele specifies attached lobes

Early Ideas About Heredity _______________ theory- –Genetic material mixes much like yellow and blue paint makes ____ Problem: –Would expect variation to ________ –Yet variation in traits _______ How are traits transmitted?

Gregor Mendel Strong background in plant breeding and mathematics- __________ Using pea plants, found indirect but observable evidence of how parents transmit ____to offspring The Garden Pea Plant Self-pollinating ______________ (different alleles not normally introduced) Can be experimentally _- ___________

What is a gene? Units of information about specific ____ Passed from _________ to offspring Each has a specific location (_____) on a chromosome What is an allele? Different ________________ of a gene Arise by _____________ Dominant allele ___________ a recessive allele that is paired with it

Vocabulary _____________ - An organism with two _______ alleles for a character (e.g. AA or aa) ___________- An organism with two ____________ alleles for a character (e.g. Aa) ________ - A description of an organism’s ______ ________ - A description of its ______________ Example- For flower color in peas, both PP and Pp plants have the same phenotype (purple) but different genotypes (homozygous and heterozygous).

_________________ P1 x P2 _________________ F1_________________ Mendel cross-pollinated peas F1 x F1 F2 The F2 generation revealed two principles of heredity: 1._____________________ 2._______________________

Mendel’s Monohybrid Cross Results 787 tall277 dwarf 651 long stem207 at tip 705 purple224 white 152 yellow428 green 299 wrinkled882 inflated 6,022 yellow2,001 green 5,474 round1,850 wrinkled F 2 plants showed dominant-to- recessive ratio that averaged 3:1

Mendel’s Law of Segregation 1.An individual inherits a unit of information (_______) about a trait from each parent 2.During gamete formation, the alleles _________ from each other

A ________________ predicts the results of a genetic cross between individuals of known genotype. PP x pp All Pp Purple White F1 Pp x Pp F2 Predicts 75% purple: 25% white Or 3:1 ratio Call the dominant allele “P” Call the recessive allele “p” 1. Law of segregation p Pp P

Dihybrid Cross Experimental cross between individuals that are homozygous for different versions of two traits AABBaabbx AaBb AB ab TRUE- BREEDING PARENTS: GAMETES : F 1 HYBRID OFFSPRING: purple flowers, tall white flowers, dwarf All purple-flowered, tall

Phenotypic Ratios in F 2 Four Phenotypes: –Tall, purple-flowered (9/16) –Tall, white-flowered (3/16) –Dwarf, purple-flowered (3/16) –Dwarf, white-flowered (1/16) AaBb X AaBbAaBb 9:3:3:1 is magic ratio in dihybrid cross

Explanation of Mendel’s Dihybrid Results If the two traits are coded for by genes on separate chromosomes, sixteen gamete combinations are possible aBaB AB abAbAb AbAb aBaB 1/4 AaBbAaBbaabbAabbaaBb AABBAABbAaBBAaBb AABbAAbbAaBbAaBbAabb AaBbAaBbaaBBaaBbAaBB 1/16

Metaphase I Metaphase II: Gametes: 1/4 AB1/4 ab1/4 Ab1/4 aB AAAA AAAA AAAA BB BB BB BB BBBB aaaa aaaa aaaa bbbb bbbb bbbb OR Law of independent assortment two “units” for the first trait were to be assorted into gametes ____________ of the two “units” for the other trait

Impact of Mendel’s Work Mendel presented his results in ____ Paper received _______________ Mendel discontinued his experiments in 1871 Paper rediscovered in ______ and finally appreciated

Dominance Relations _____________dominance ____________ dominance –Heterozygote phenotype is somewhere ___________that of two homozyotes _________________ –Non-identical alleles specify two ______________ that are both expressed in ________________

1. ___________________ -one of every 2,500 whites of European descent. –One in 25 whites is a _______________ –The normal allele codes for a membrane protein that transports Cl - between cells and the environment. –If these channels are defective or absent, there are abnormally high extracellular levels of chloride that causes the mucus coats of certain cells to become thicker and stickier than normal. –This mucus build-up in the pancreas, lungs, digestive tract, and elsewhere favors bacterial infections. –Without treatment, affected children die before five, but with treatment can live past their late 20’s. Examples of recessive disorders

2. Tay-Sachs disease –Caused by a dysfunctional enzyme that fails to break down specific brain lipids. –Symptoms- seizures, blindness, and degeneration of motor and mental performance a few months after birth. –Child dies after a few years. –Among Ashkenazic Jews (those from central Europe) this disease occurs in one of 3,600 births, about 100 times greater than the incidence among non-Jews or Mediterranean (Sephardic) Jews. Examples of recessive disorders

Flower Color in Snapdragons: Pink-flowered plant X Pink-flowered plant White-, pink-, and red-flowered plants in a 1:2:1 ratio (heterozygote) Pink flowers have one normal and one ____________allele __________________ Dominance

Genetics of ABO Blood Types: ______Alleles Gene that controls ABO type codes for enzyme that dictates structure of a glycolipid on blood cells Two alleles (I A and I B ) are ________ when paired Third allele (i) is _________ to others Codominance Type A - I A I A or I a i Type B - I B I B or I B i Type AB - I A I B Type O - ii

ABO and Transfusions Recipient’s immune system will attack blood cells that have an unfamiliar glycolipid on surface Type __ is universal donor because it has neither type A nor type B glycolipid

Pleitropy Alleles at a ______ locus may have effects on _______________ traits Classic example is the effects of the mutant allele at the _______________ that gives rise to sickle-cell anemia Hb S homozygotes produce only the ___________hemoglobin; suffer from sickle-cell anemia At low ___ levels, cells with only Hb S hemoglobin “sickle” and stick together- clog __________- Eye disease, infection, heart disease

Fig , p. 161

Albinism ________ production is completely blocked Homozygous recessive at the gene locus that codes for _____

Human Variation Some human traits occur as a few ________types –Attached or detached earlobes –Many genetic disorders Other traits show continuous variation –________ –Weight –Eye color

Describing Continuous Variation Range of values for the trait Number of individuals with some value of the trait (line of bell-shaped curve indicates continuous variation in population) Range of values for the trait Number of individuals with some value of the trait

Temperature Effects on Phenotype Himalayan rabbits are Homozygous for an allele that specifies a heat- sensitive version of an enzyme in melanin- producing pathway Melanin is produced in cooler areas of body